1. Field of the Invention
This invention relates to a method and an apparatus for continuously coating particles in a turning fluidized bed, and more particularly to a method and an apparatus for continuously coating discrete solid particles in a turning fluidized bed formed in a cylindrical vessel or container the bottom of which is constituted by a rotary disk and into which hot air is blown through a number of air blow holes provided between the peripheral edge of the rotary disk and the side wall of the cylindrical vessel.
The techniques of coating discrete particles with a desired coating material are sorted to, for example, in the production of agricultural chemicals to impart porousness to carrier particle surfaces for increasing its capacity of retaining chemical components, in the pharmaceutical field to facilitate oral administration of doses, stabilize chemical components or adjust the point of producing a particular medicinal effect or effects, or in the manufacture of ceramic materials to improve the surface quality of particulate raw materials.
2. Description of the Prior Art
There have thus far been proposed various kinds of apparatus for coating discrete particles, among which the fluidised bed type coating apparatus are most widely adopted for their superiority in the ability of mixing particular raw material, uniformity of coated films and coating efficiency, so that batch type and continuously type coating apparatuses are put to practical use.
However, in the conventional fluidised bed coating processes, the particles are desired to have a particle size greater than 300 .mu.m since otherwise they would tend to gather and make the coating operation difficult. Therefore, materials of smaller particle sizes are generally coated batchwise in a turning fluidised bed.
The batch type turning fluidised bed usually employs a cylindrical vessel which has a rotary disk at its bottom, and particles of a raw material are coated in a turning fluidised bed which is formed by blowing in hot air through gaps between the peripheral edge portions of the disk and cylindrical side walls of the vessel. This turning fluidised bed perimits to coat very fine particles without causing agglomeration of the particles, but it still involves a problem that the batchwise operation lacks efficiency. Accordingly, there has been a strong demand for the development of a continuous coating process which can be industrially applied for the production of coated particles even of the small particle sizes as mentioned above on a large scale.